Messages in this thread | | | From | "Vaittinen, Matti" <> | Subject | Re: [PATCH v3 1/7] clkdev: Hold clocks_mutex while iterating clocks list | Date | Fri, 5 Apr 2019 06:51:43 +0000 |
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Hello Stephen,
Thanks for taking care of this!
On Thu, 2019-04-04 at 14:53 -0700, Stephen Boyd wrote: > We recently introduced a change to support devm clk lookups. That > change > introduced a code-path that used clk_find() without holding the > 'clocks_mutex'. Unfortunately, clk_find() iterates over the 'clocks' > list and so we need to prevent the list from being modified while > iterating over it by holding the mutex. Similarly, we don't need to > hold > the 'clocks_mutex' besides when we're dereferencing the clk_lookup > pointer
/// Snip
> -out: > +static struct clk_lookup *clk_find(const char *dev_id, const char > *con_id) > +{ > + struct clk_lookup *cl; > + > + mutex_lock(&clocks_mutex); > + cl = __clk_find(dev_id, con_id); > mutex_unlock(&clocks_mutex); > > - return cl ? clk : ERR_PTR(-ENOENT); > + return cl; > +}
I am not an expert on this but reading commit message abowe and seeing the code for clk_find() looks a bit scary. If I understand it correctly, the clocks_mutex should be held when dereferencing the clk_lookup returned by clk_find. The clk_find implementation drops the lock before returning - which makes me think I miss something here. How can the caller ever safely dereference returned clk_lookup pointer? Just reading abowe makes me think that lock should be taken by whoever is calling the clk_find, and dropped only after caller has used the found clk_lookup for whatever caller intends to use it. Maybe I am missing something?
Br, Matti Vaittinen
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